COMPRESSED AIR-DRIVEN TOOL
A compressed air-driven tool having an electromagnetically operated control element (27) for controlling a pneumatic control circuit in order to maintain a load-independent torque at a constant rotational speed. The tool includes a principal valve (5), which arranged in a drive housing (1) in a manner displaceable by the supplied compressed air against the force of a helical spring (13), and a generator (43), which is mounted on the shaft (49) of a turbine wheel (51). The rotational speed of the shaft (49) is measured with a speed sensor (75) and the supply of compressed air to the principal valve (5) is controlled in the event of a drop in rotational speed as a consequence of a load.
Latest Otto Suhner AG Patents:
The invention relates to a compressed air-driven tool.
BACKGROUNDCompressed air-driven tools are used primarily in the metal-processing industry and are distinguished by a relatively low weight in relation to the power, since no drive motor, such as an electric motor, is arranged within the tool and, in particular in the case of hand-operated tools, leads to rapid fatigue of the operator.
The rotational speed regulation for such tools is complex and has hitherto been performed by centrifugal force regulators which, in the idle state, throttle the supply of air and, under loading, open it up again. The currently required reliability and the maintenance of constant rotational speed in the case of changing work processes and conditions cannot be achieved.
In U.S. Pat. No. 6,908,277, a description is furthermore given of a rotational speed regulator for a rotating compressed-air motor. In the case of said rotational speed regulator, there is arranged on the shaft of the tool a generator which, in a manner dependent on the rotational speed of the shaft, generates a correspondingly variable output voltage. An electromagnetic adjustment element is fed with the respective output voltage in order to control the inlet valve for compressed air at the tool in a manner directly dependent on the output voltage. In this known embodiment, the centrifugal force element is replaced by an electromagnetic actuated adjustment element. That is to say, for the actuation of the electromagnetic adjustment element, a voltage is generated within the tool, with the result that said adjustment element manages without an external current source.
A disadvantage of this rotational speed regulation is the fact that the regulation of the working rotational speed is dependent on the variable voltage which is generated by the motor shaft. This means that the maintenance of the rotational speed of the tool, in particular in the case of variable load, is not possible or is possible only to an insufficient extent.
A fluid-powered medical, in particular dental, hand grip is known from EP 2 449 999. The determination of the actual value of the rotational speed is realized via the amplitude of the rectified generator voltage (analog), and the adjustment element is designed as a proportional valve or as a throttle. This procedure is adequate for fluid drives in the medical sector, in the case of which it is necessary for very low torques to be generated, but not for tools of the metal-processing industry.
A pneumatically powered hand tool in which, via an internal battery and a microcomputer, it is possible for an electromagnetic valve to be controlled directly in the supply-air duct is furthermore known from US 2001/0088921. The battery is fed by a generator in the waste-air stream, the generated energy of which generator is not sufficient for the actuation of an electromagnetic valve.
A further medical handpiece in which, for the purpose of control, use is made of an electrical energy source such as a constant-current source and/or a constant-voltage source, that is to say an external current source, is known from EP 2 727 552. A current connection which is intended to be avoided by the tool according to the invention is indispensable here.
SUMMARYAn object of the present invention is the provision of a compressed air-driven tool, for which the set rotational speed is able to be set exactly to a settable value even under the influence of disturbance variables such as load.
A further object of the invention is the immediate drop in the rotational speed to a non-hazardous value which is minimal for the tool and the workpiece in the event of the current being cut off due to failure of the internal generator.
This object is achieved by a compressed air-driven tool having one or more features of the invention. Advantageous configurations of the tool are described below and in the claims.
A voltage regulator makes it possible for a constant output voltage for feeding a microcontroller to be generated independently of the present variable rotational speed, adapted to the work to be performed, of the shaft. Consequently, it is thus possible, in a manner dependent on the measured rotational speed of the motor and independently of the load of the tool, for the electromagnetic control element to control the air passage at the inlet valve and for the selected rotational speed to be maintained in the case of variable load. The internally generated voltage serves only for feeding the microcontroller and the inlet valve.
The invention will be described in more detail on the basis of two illustrated exemplary embodiments. In the figures:
A schematic illustration with reference sign 1 is given of the drive housing with the drive elements of the compressed air-driven tool. One possible construction of the tool is illustrated in
The build-up of an operating voltage for the microcontroller 37 is realized in the supply air stream via a generator 43 whose windings 45 can be fastened for example to the housing 1 and interact with a rotor 47. The rotor 47 is arranged on the shaft 49 of the turbine wheel 51. The turbine wheel 51 is supported by at least one bearing 53 on the housing 1. From the generator 43, the alternating-current voltage generated there is fed to a rectifier 55. The rectifier 55 is furthermore connected to a voltage regulator 57, which feeds the microcontroller 37 with a constant direct-current voltage which is independent of the present rotational speed of the shaft 49 of the turbine wheel 51. The turbine wheel 51 may, as illustrated in the figures, be arranged directly on the output shaft 49 of the tool or in a bypass at the supply duct 61 for compressed air to the turbine wheel 51 (not shown).
The turbine wheel 51, with its blades 59 (not illustrated in detail, but purely schematically), is driven by the supply air stream which is conducted through the supply duct 61. The supply duct 61 is connected to the bore 7 in the housing 1. The mouth of the supply duct 61 into the bore 7 is situated in a first ring-shaped recess 67 in the bore 7. In addition to the supply duct 61, which opens into the bore 7 from below in the figures, a further supply duct 61′ may be led into the blade space 63, in which the blades 59 revolve. The second supply duct 61′ opens in an axially offset manner into the bore 7 in the second ring-shaped recess 69. The two ring-shaped recesses 67 and 69 are covered in the unpressurized region, that is to say without supply of compressed air or with supply of compressed air, said region having a piston-like form.
In the first exemplary embodiment as per
The functioning of the electronic control of the compressed-air tool as per the first exemplary embodiment will be described below.
Prior to commencing work with the tool, that is to say before compressed air is supplied to the turbine wheel 51 through the inlet duct 3, for example from the operating power supply system, the main valve 5 is situated in the position illustrated in
The space 14 in the bore 7, in which the helical spring 13 is arranged, is kept unpressurized or at atmospheric pressure by a venting opening 77 which is connected to the atmosphere. The ring-shaped head space 17 behind the first sealing region 9 is, at this time, connected via the first venting duct 19 to the valve space 21 and via the second venting duct 23 likewise to the atmosphere, and is unpressurized. The pressure duct 25, which leads from the bore 7 into the valve space 21, is closed off by the regulating valve 27, or the sealing element 30 thereof, at the second end 27″. As soon as the operating voltage Vi required for the operation of the microcontroller 37 has been reached, the rotational speed preset by the potentiometer 39 can be attained by activation and deactivation of the electromagnet 33. The rotational speed is measured by a suitable rotational speed sensor 75 on the shaft 49. The activation and deactivation of the electromagnet 33 brings about, in an alternating manner, the opening and closing of the pressure duct 25 and of the second venting duct 23, and consequently oscillation of the regulating valve 27. The charging of the main valve 5 with compressed air that is consequently brought about is described below. If a load is then applied to the shaft 49, then the rotational speed initially drops. In order to be able to compensate this, that is to say to increase the torque in order to maintain the desired rotational speed, the regulating valve 27 is pivoted clockwise by way of the microcontroller 37 by corresponding activation of the electromagnet 33, whereby compressed air can flow from the air inlet 3 via the ring-shaped groove 65 through the pressure duct 25 into the valve space 21 and, from there, further through the first venting duct 19 into the ring-shaped space 17 behind the first sealing region 9 (
The second configuration of the pressure-driven tool as per
In practice, it is expedient for use to be made of a larger regulating valve for the second configuration variant, in order to be able to compensate for the constant waste-air stream brought about by the throttle.
Illustrated in the graphical illustrations in
In the illustration as per
The profile of the voltage at the generator 43 is illustrated in
The measurement of the rotational speed is realized as per
Claims
1. A method for regulating a rotational speed of an output shaft (49) at a tool which is driven with compressed air, the method comprising:
- using a generator (43) driven by the compressed air, in the tool, and generating an alternating-current voltage;
- activating an electromagnetic regulating element (27) using the alternating-current voltage by which a quantity of air for the drive of a turbine wheel (51) on the output shaft (49) is regulated,
- converting the alternating-current voltage into a direct-current voltage in a rectifier (55),
- maintaining the direct-current voltage constant using a voltage regulator (57) independently of the rotational speed of the output shaft (49),
- feeding a microcontroller (37) with the constant direct-current voltage, measuring a present value of the rotational speed of the output shaft (49) using a rotational speed sensor (75), and
- the microcontroller (37) regulating, by way of the electromagnetically driven regulating valve (27), the quantity of air supplied to the turbine wheel (51) and keeping a set predefined rotational speed of the shaft (49) constant.
2. The method as claimed in claim 1, further comprising using the quantity of air regulated by the regulating valve (27) to control a main valve (5) which is displaceably inserted in a bore (7) in the housing (1) of the tool to regulate the inflow of air to the turbine wheel (51) by completely or partially opening up one or more supply ducts (61, 61′) for the compressed air during the displacement of the main valve (5), and the quantity of air at the turbine wheel (51) is increased in case of an increase in load at the output shaft (49) and the predefined rotational speed is maintained.
3. A compressed air-driven tool comprising:
- a drive housing (1) which includes a turbine wheel (51) that drives a output shaft (49),
- an air inlet duct (3) for compressed air,
- a waste-air duct (73),
- a generator (43) inserted in a supply air path for the compressed air that is adapted to generate an electrical alternating-current voltage,
- a rectifier (55) that is configured to convert the electrical alternating-current voltage to a direct-current voltage,
- a microcontroller (37),
- a rotational speed sensor for the output shaft, and
- a voltage regulator configured to generate a constant output voltage, which is independent of a rotational speed of the shaft (49), for operation of the microcontroller (37) which is configured to control a control element (27) for the actuation of a main valve (5) based on measurement data of the rotational speed sensor (75) for the output shaft (49).
4. The compressed air-driven tool as claimed in claim 3, wherein the generator (43) is arranged on the output shaft (49) or on a second shaft, which is independent of the output shaft (49), in a bypass.
5. The compressed air-driven tool as claimed in claim 4, further comprising a bore (7) that accommodates the main valve (5) formed in the drive housing (1), the bore (7) is formed so as to be connectable by an air inlet (3) to a compressed-air source, and the bore (7) is connected by a pressure duct (25) and by a first venting duct (19) to a valve space (21), and an electromagnetically activatable regulating valve (27) for opening and closing the pressure duct (25), or for closing a second venting duct (23), is inserted in the valve space (21), and the regulating valve (27) is configured to be regulated in a manner dependent on the rotational speed of the shaft (49), which is measured by the rotational speed sensor (75).
6. The compressed air-driven tool as claimed in claim 5, wherein the main valve (5) is displaceably guided between a head space (17) and an unpressurized space (14) in the bore (7).
7. The compressed air-driven tool as claimed in claim 5, wherein the valve space (21) is connected by the first venting duct (19) to a bottom-side head space (17) at a bottom of the main valve (5).
8. The compressed air-driven tool as claimed in claim 5, wherein the valve space (21) is connected by the second venting duct (23) to the surroundings.
9. The compressed air-driven tool as claimed in claim 6, wherein the main valve (5) comprises first (9) and second flange-shaped sealing regions (11) that are spaced apart from one another, shell surfaces of which bear slidingly against a wall of the bore (7), and a helical spring (13) inserted in an unpressurized space (14) in the bore (7), the helical spring (13) being inserted between the main valve (5) and a wall delimiting the bore (7) on an end side.
10. The compressed air-driven tool as claimed in claim 9, wherein the first sealing region (9) sealingly guides the main valve (5) on the head side with respect to the bore (7), the second sealing region (11) is arranged such that a first mouth into the bore (7) of a first supply duct (61) is partially closed off, and a mouth of a second supply duct (61′) is completely closed off, for the main valve (5) in an unpressurized state on the head space side or the pressure space side.
11. The compressed air-driven tool as claimed in claim 10, wherein at least one of the air inlet duct (3), the first (61), or the second supply duct (61′) in each case open into a ring-shaped groove (65) or a first recess (67) or a second recess (69) at the main valve (5).
12. The compressed air-driven tool as claimed in claim 11, wherein the supply ducts (61, 61′) open into a blade space (63) of a turbine wheel (51).
13. The compressed air-driven tool as claimed in claim 3, wherein the regulating valve (27) in the valve space (21) is mounted pivotably such that either the pressure duct (25) or the second venting duct (23) is closed off by a sealing element (28, 30) which is actuated by an electromagnet (33) and which is attached to the regulating valve (27).
14. The compressed air-driven tool as claimed in claim 3, wherein the rotational speed measurement is calculated by detecting a time difference in rising flanks of an alternating current signal.
Type: Application
Filed: Jun 19, 2018
Publication Date: Jul 9, 2020
Patent Grant number: 11607788
Applicant: Otto Suhner AG (Brugg)
Inventors: Stefan WIEDEMEIER (Brugg Aargau), Stefan INEICHEN (Niederlenz Aargau)
Application Number: 16/623,120